Prostate Cancer
Prostate cancer is the most prevalent cancer in men and is the second leading cause of death from cancer among males in the United States. AJCC Cancer Staging Handbook 203 (Irvin D. Fleming et al. eds., 5th ed. 1998); Walter J. Burdette, Cancer: Etiology Diagnosis, and Treatment 147 (1998). In 1999, it was estimated that 37,000 men in the United States would die as result of prostate cancer. Elizabeth A. Platz et al., & Edward Giovannucci, Epidemiology of and Risk Factors for Prostate Cancer, in Management of Prostate Cancer 21 (Eric A Klein, ed. 2000). More recently, the American Cancer Society estimated there will be 230,110 new cases of prostate cancer and 29,900 deaths in 2004. American Cancer Society website: cancer.org of the world wide web. Cancer of the prostate typically occurs in older males, with a median age of 74 years for clinical diagnosis. Burdette, supra at 147. A man's risk of being diagnosed with invasive prostate cancer in his lifetime is one in six. Platz et al., supra at 21.
Although our understanding of the etiology of prostate cancer is incomplete, the results of extensive research in this area point to a combination of age, genetic and environmental/dietary factors. Platz et al., supra at 19; Burdette, supra at 147; Steven K. Clinton, Diet and Nutrition in Prostate Cancer Prevention and Therapy, in Prostate Cancer: a Multidisciplinary Guide 246-269 (Philip W. Kantoff et al. eds. 1997). Broadly speaking, genetic risk factors predisposing one to prostate cancer include race and a family history of the disease. Platz et al., supra at 19, 28-29, 32-34. Aside from these generalities, a deeper understanding of the genetic basis of prostate cancer has remained elusive. Considerable research has been directed to studying the link between prostate cancer, androgens, and androgen regulation, as androgens play a crucial role in prostate growth and differentiation. Meena Augustus et al., Molecular Genetics and Markers of Progression, in Management of Prostate Cancer 59 (Eric A Klein ed. 2000). While a number of studies have concluded that prostate tumor development is linked to elevated levels of circulating androgen (e.g., testosterone and dihydrotestosterone), the genetic determinants of these levels remain unknown. Platz et al., supra at 29-30.
Several studies have explored a possible link between prostate cancer and the androgen receptor (AR) gene, the gene product of which mediates the molecular and cellular effects of testosterone and dihydrotestosterone in tissues responsive to androgens. Id. at 30. Differences in the number of certain trinucleotide repeats in exon 1, the region involved in transactivational control, have been of particular interest. Augustus et al., supra at 60. For example, these studies have revealed that as the number of CAG repeats decreases the transactivation ability of the gene product increases, as does the risk of prostate cancer. Platz et al., supra at 30-31. Other research has focused on the α-reductase Type 2 gene, the gene which codes for the enzyme that converts testosterone into dihydrotestosterone. Id. at 30. Dihydrotestosterone has greater affinity for the AR than testosterone, resulting in increased transactivation of genes responsive to androgens. Id. While studies have reported differences among the races in the length of a TA dinucleotide repeat in the 3′ untranslated region, no link has been established between the length of that repeat and prostate cancer. Id. Interestingly, while ras gene mutations are implicated in numerous other cancers, such mutations appear not to play a significant role in prostate cancer, at least among Caucasian males. Augustus, supra at 52.
Environmental/dietary risk factors which may increase the risk of prostate cancer include intake of saturated fat and calcium. Platz et al., supra at 19, 25-26. Conversely, intake of selenium, vitamin E and tomato products (which contain the carotenoid lycopene) apparently decrease that risk. Id. at 19, 26-28 The impact of physical activity, cigarette smoking, and alcohol consumption on prostate cancer is unclear. Platz et al., supra at 23-25.
Periodic screening for prostate cancer is most effectively performed by digital rectal examination (DRE) of the prostate, in conjunction with determination of the serum level of prostate-specific antigen (PSA). Burdette, supra at 148. While the merits of such screening are the subject of considerable debate, Jerome P. Richie & Irving D. Kaplan, Screening for Prostate Cancer. The Horns of a Dilemma, in Prostate Cancer: A Multidisciplinary Guide 1-10 (Philip W. Kantoff et al. eds. 1997), the American Cancer Society and American Urological Association recommend that both of these tests be performed annually on men 50 years or older with a life expectancy of at least 10 years, and younger men at high risk for prostate cancer. Ian M. Thompson & John Foley, Screening for Prostate Cancer, in Management of Prostate Cancer 71 (Eric A Klein ed. 2000). If necessary, these screening methods may be followed by additional tests, including biopsy, ultrasonic imaging, computerized tomography, and magnetic resonance imaging. Christopher A. Haas & Martin I. Resnick, Trends in Diagnosis, Biopsy, and Imaging, in Management of Prostate Cancer 89-98 (Eric A Klein ed. 2000); Burdette, supra at 148.
Once the diagnosis of prostate cancer has been made, treatment decisions for the individual are typically linked to the stage of prostate cancer present in that individual, as well as his age and overall health. Burdette, supra at 151. One preferred classification system for staging prostate cancer was developed by the American Urological Association (AUA). Id. at 148. The AUA classification system divides prostate tumors into four broad stages, A to D, which are in turn accompanied by a number of smaller substages. Burdette, supra at 152-153; Anthony V. D+Amico et al., The Staging of Prostate Cancer, in Prostate Cancer: A Multidisciplinary Guide 41 (Philip W. Kantoff et al. eds. 1997).
Stage A prostate cancer refers to the presence of microscopic cancer within the prostate gland. D+Amico, supra at 41. This stage is comprised of two substages: A1, which involves less than four well-differentiated cancer foci within the prostate, and A2, which involves greater than three well-differentiated cancer foci or alternatively, moderately to poorly differentiated foci within the prostate. Burdette, supra at 152; D+Amico, supra at 41. Treatment for stage A1 preferentially involves following PSA levels and periodic DRE. Burdette, supra at 151. Should PSA levels rise, preferred treatments include radical prostatectomy in patients 70 years of age and younger, external beam radiotherapy for patients between 70 and 80 years of age, and hormone therapy for those over 80 years of age. Id.
Stage B prostate cancer is characterized by the presence of a palpable lump within the prostate. Burdette, supra at 152-53; D+Amico, supra at 41. This stage is comprised of three substages: B1, in which the lump is less than 2 cm and is contained in one lobe of the prostate; B2, in which the lump is greater than 2 cm yet is still contained within one lobe; and B3, in which the lump has spread to both lobes. Burdette, supra, at 152-53. For stages B1 and B2, the treatment again involves radical prostatectomy in patients 70 years of age and younger, external beam radiotherapy for patients between 70 and 80 years of age, and hormone therapy for those over 80 years of age. Id. at 151. In stage B3, radical prostatectomy is employed if the cancer is well-differentiated and PSA levels are below 15 ng/mL; otherwise, external beam radiation is the chosen treatment option. Id.
Stage C prostate cancer involves a substantial cancer mass accompanied by extraprostatic extension. Burdette, supra at 153; D'Amico, supra at 41. Like stage A prostate cancer, Stage C is comprised of two substages: substage C1, in which the tumor is relatively minimal, with minor prostatic extension, and substage C2, in which the tumor is large and bulky, with major prostatic extension. Id. The treatment of choice for both substages is external beam radiation. Burdette, supra at 151.
The fourth and final stage of prostate cancer, Stage D, describes the extent to which the cancer has metastasized. Burdette, supra at 153; D'Amico, supra at 41. This stage is comprised of four substages: (1) D0, in which acid phophatase levels are persistently high, (2) D1, in which only the pelvic lymph nodes have been invaded, (3) D2, in which the lymph nodes above the aortic bifurcation have been invaded, with or without distant metastasis, and (4) D3, in which the metastasis progresses despite intense hormonal therapy. Id. Treatment at this stage may involve hormonal therapy, chemotherapy, and removal of one or both testes. Burdette, supra at 151.
Despite the need for accurate staging of prostate cancer, current staging methodology is limited. The wide variety of biological behavior displayed by neoplasms of the prostate has resulted in considerable difficulty in predicting and assessing the course of prostate cancer. Augustus et al., supra at 47. Indeed, despite the fact that most prostate cancer patients have carcinomas that are of intermediate grade and stage, prognosis for these types of carcinomas is highly variable. Andrew A Renshaw & Christopher L. Corless, Prognostic Features in the Pathology of prostate Cancer, in Prostate Cancer: A Multidisciplinary Guide 26 (Philip W. Kantoff et al. eds. 1997). Techniques such as transrectal ultrasound, abdominal and pelvic computerized tomography, and MRI have not been particularly useful in predicting local tumor extension. D+Amico, supra at 53 (editors' comment). While the use of serum PSA in combination with the Gleason score is currently the most effective method of staging prostate cancer, id., PSA is of limited predictive value, Augustus et al., supra at 47; Renshaw et al., supra at 26, and the Gleason score is prone to variability and error, King, C. R. & Long, J. P., Int'l. J. Cancer 90(6): 326-30 (2000). As such, the current focus of prostate cancer research has been to obtain biomarkers to help better assess the progression of the disease. Augustus et al., supra at 47; Renshaw et al., supra at 26; Pettaway, C. A., Tech. Urol. 4(1): 35-42 (1998).
Accordingly, there is a great need for more sensitive and accurate methods for predicting whether a person is likely to develop prostate cancer, for diagnosing prostate cancer, for monitoring the progression of the disease, for staging the prostate cancer, for determining whether the prostate cancer has metastasized and for imaging the prostate cancer. There is also a need for better treatment of prostate cancer.
Ovarian Cancer
Cancer of the ovaries is the fourth-most common cause of cancer death in women in the United States, with more than 23,000 new cases and roughly 14,000 deaths predicted for the year 2001. Shridhar, V. et al., Cancer Res. 61(15): 5895-904 (2001); Memarzadeh, S. & Berek, J. S., J. Reprod. Med. 46(7): 621-29 (2001). The American Cancer Society estimates that there will be about 25,580 new cases of ovarian cancer in 2004 in the United States alone. Ovarian cancer will cause about 16,090 deaths in the United States in the same year. ACS Website: cancer.org of the world wide web. The incidence of ovarian cancer is of serious concern worldwide, with an estimated 191,000 new cases predicted annually. Runnebaum, I. B. & Stickeler, E., J. Cancer Res. Clin. Oncol. 127(2): 73-79 (2001). Unfortunately, women with ovarian cancer are typically asymptomatic until the disease has metastasized. Because effective screening for ovarian cancer is not available, roughly 70% of women diagnosed have an advanced stage of the cancer with a five-year survival rate of 25-30%. Memarzadeh, S. & Berek, J. S., supra; Nunns, D. et al., Obstet. Gynecol. Surv. 55(12): 746-51. Conversely, women diagnosed with early stage ovarian cancer enjoy considerably higher survival rates. Werness, B. A. & Eltabbakh, G. H., Int'l. J. Gynecol. Pathol. 20(1): 48-63 (2001). Although our understanding of the etiology of ovarian cancer is incomplete, the results of extensive research in this area point to a combination of age, genetics, reproductive, and dietary/environmental factors. Age is a key risk factor in the development of ovarian cancer: while the risk for developing ovarian cancer before the age of 30 is slim, the incidence of ovarian cancer rises linearly between ages 30 to 50, increasing at a slower rate thereafter, with the highest incidence being among septagenarian women. Jeanne M. Schilder et al., Hereditary Ovarian Cancer: Clinical Syndromes and Management, in Ovarian Cancer 182 (Stephen C. Rubin & Gregory P. Sutton eds., 2d ed. 2001).
With respect to genetic factors, a family history of ovarian cancer is the most significant risk factor in the development of the disease, with that risk depending on the number of affected family members, the degree of their relationship to the woman, and which particular first degree relatives are affected by the disease. Id. Mutations in several genes have been associated with ovarian cancer, including BRCA1 and BRCA2, both of which play a key role in the development of breast cancer, as well as hMSH2 and hMLH1, both of which are associated with hereditary non-polyposis colon cancer. Katherine Y. Look, Epidemiology, Etiology, and Screening of Ovarian Cancer, in Ovarian Cancer 169, 171-73 (Stephen C. Rubin & Gregory P. Sutton eds., 2d ed. 2001). BRCA1, located on chromosome 17, and BRCA2, located on chromosome 13, are tumor suppressor genes implicated in DNA repair; mutations in these genes are linked to roughly 10% of ovarian cancers. Id. at 171-72; Schilder et al., supra at 185-86. hMSH2 and hMLH1 are associated with DNA mismatch repair, and are located on chromosomes 2 and 3, respectively; it has been reported that roughly 3% of hereditary ovarian carcinomas are due to mutations in these genes. Look, supra at 173; Schilder et al., supra at 184, 188-89.
Reproductive factors have also been associated with an increased or reduced risk of ovarian cancer. Late menopause, nulliparity, and early age at menarche have all been linked with an elevated risk of ovarian cancer. Schilder et al., supra at 182. One theory hypothesizes that these factors increase the number of ovulatory cycles over the course of a woman's life, leading to “incessant ovulation,” which is thought to be the primary cause of mutations to the ovarian epithelium. Id.; Laura J. Havrilesky & Andrew Berchuck, Molecular Alterations in Sporadic Ovarian Cancer, in Ovarian Cancer 25 (Stephen C. Rubin & Gregory P. Sutton eds., 2d ed. 2001). The mutations may be explained by the fact that ovulation results in the destruction and repair of that epithelium, necessitating increased cell division, thereby increasing the possibility that an undetected mutation will occur. Id. Support for this theory may be found in the fact pregnancy, lactation, and the use of oral contraceptives, all of which suppress ovulation, confer a protective effect with respect to developing ovarian cancer. Id.
Among dietary/environmental factors, there would appear to be an association between high intake of animal fat or red meat and ovarian cancer, while the antioxidant Vitamin A, which prevents free radical formation and also assists in maintaining normal cellular differentiation, may offer a protective effect. Look, supra at 169. Reports have also associated asbestos and hydrous magnesium trisilicate (talc), the latter of which may be present in diaphragms and sanitary napkins. Id. at 169-70.
Current screening procedures for ovarian cancer, while of some utility, are quite limited in their diagnostic ability, a problem that is particularly acute at early stages of cancer progression when the disease is typically asymptomatic yet is most readily treated. Walter J. Burdette, Cancer: Etiology, Diagnosis, and Treatment 166 (1998); Memarzadeh & Berek, supra; Runnebaum & Stickeler, supra; Werness & Eltabbakh, supra. Commonly used screening tests include biannual rectovaginal pelvic examination, radioimmunoassay to detect the CA-125 serum tumor marker, and transvaginal ultrasonography. Burdette, supra at 166.
Pelvic examination has failed to yield adequate numbers of early diagnoses, and the other methods are not sufficiently accurate. Id. One study reported that only 15% of patients who suffered from ovarian cancer were diagnosed with the disease at the time of their pelvic examination. Look, supra at 174. Moreover, the CA-125 test is prone to giving false positives in pre-menopausal women and has been reported to be of low predictive value in post-menopausal women. Id. at 174-75. Although transvaginal ultrasonography is now the preferred procedure for screening for ovarian cancer, it is unable to distinguish reliably between benign and malignant tumors, and also cannot locate primary peritoneal malignancies or ovarian cancer if the ovary size is normal. Schilder et al., supra at 194-95. While genetic testing for mutations of the BRCA1, BRCA2, hMSH2, and hMLH1 genes is now available, these tests may be too costly for some patients and may also yield false negative or indeterminate results. Schilder et al., supra at 191-94.
Other markers of interest are HE4 and mesothelin, see Urban et al. Ovarian cancer screening Hematol Oncol Clin North Am. 2003 August; 17(4):989-1005; Hellstrom et al. The HE4 (WFDC2) protein is a biomarker for ovarian carcinoma, Cancer Res. 2003 Jul. 1;63(13):3695-700; Ordonez, Application of mesothelin immunostaining in tumor diagnosis, Am J Surg Pathol. 2003 November; 27(11):1418-28.
The staging of ovarian cancer, which is accomplished through surgical exploration, is crucial in determining the course of treatment and management of the disease. AJCC Cancer Staging Handbook 187 (Irvin D. Fleming et al. eds., 5th ed. 1998); Burdette, supra at 170; Memarzadeh & Berek, supra; Shridhar et al., supra. Staging is performed by reference to the classification system developed by the International Federation of Gynecology and Obstetrics. David H. Moore, Primary Surgical Management of Early Epithelial Ovarian Carcinoma, in Ovarian Cancer 203 (Stephen C. Rubin & Gregory P. Sutton eds., 2d ed. 2001); Fleming et al. eds., supra at 188. Stage I ovarian cancer is characterized by tumor growth that is limited to the ovaries and is comprised of three substages. Id. In substage IA, tumor growth is limited to one ovary, there is no tumor on the external surface of the ovary, the ovarian capsule is intact, and no malignant cells are present in ascites or peritoneal washings. Id. Substage IB is identical to A1, except that tumor growth is limited to both ovaries. Id. Substage IC refers to the presence of tumor growth limited to one or both ovaries, and also includes one or more of the following characteristics: capsule rupture, tumor growth on the surface of one or both ovaries, and malignant cells present in ascites or peritoneal washings. Id.
Stage II ovarian cancer refers to tumor growth involving one or both ovaries, along with pelvic extension. Id. Substage IIA involves extension and/or implants on the uterus and/or fallopian tubes, with no malignant cells in the ascites or peritoneal washings, while substage IIB involves extension into other pelvic organs and tissues, again with no malignant cells in the ascites or peritoneal washings. Id. Substage IIC involves pelvic extension as in IIA or IIB, but with malignant cells in the ascites or peritoneal washings. Id.
Stage III ovarian cancer involves tumor growth in one or both ovaries, with peritoneal metastasis beyond the pelvis confirmed by microscope and/or metastasis in the regional lymph nodes. Id. Substage IIIA is characterized by microscopic peritoneal metastasis outside the pelvis, with substage IIIB involving macroscopic peritoneal metastasis outside the pelvis 2 cm or less in greatest dimension. Id. Substage IIIC is identical to IIIB, except that the metastasis is greater than 2 cm in greatest dimension and may include regional lymph node metastasis. Id. Lastly, Stage IV refers to the presence distant metastasis, excluding peritoneal metastasis. Id.
While surgical staging is currently the benchmark for assessing the management and treatment of ovarian cancer, it suffers from considerable drawbacks, including the invasiveness of the procedure, the potential for complications, as well as the potential for inaccuracy. Moore, supra at 206-208, 213. In view of these limitations, attention has turned to developing alternative staging methodologies through understanding differential gene expression in various stages of ovarian cancer and by obtaining various biomarkers to help better assess the progression of the disease. Vartiainen, J. et al., Int'l J. Cancer, 95(5): 313-16 (2001); Shridhar et al. supra; Baekelandt, M. et al., J. Clin. Oncol. 18(22): 3775-81.
The treatment of ovarian cancer typically involves a multiprong attack, with surgical intervention serving as the foundation of treatment. Dennis S. Chi & William J. Hoskins, Primary Surgical Management of Advanced Epithelial Ovarian Cancer, in Ovarian Cancer 241 (Stephen C. Rubin & Gregory P. Sutton eds., 2d ed. 2001). For example, in the case of epithelial ovarian cancer, which accounts for ˜90% of cases of ovarian cancer, treatment typically consists of: (1) cytoreductive surgery, including total abdominal hysterectomy, bilateral salpingo-oophorectomy, omentectomy, and lymphadenectomy, followed by (2) adjuvant chemotherapy with paclitaxel and either cisplatin or carboplatin. Eltabbakh, G. H. & Awtrey, C. S., Expert Op. Pharmacother. 2(10): 109-24. Despite a clinical response rate of 80% to the adjuvant therapy, most patients experience tumor recurrence within three years of treatment. Id. Certain patients may undergo a second cytoreductive surgery and/or second-line chemotherapy. Memarzadeh & Berek, supra.
From the foregoing, it is clear that procedures used for detecting, diagnosing, monitoring, staging, prognosticating, and preventing the recurrence of ovarian cancer are of critical importance to the outcome of the patient. Moreover, current procedures, while helpful in each of these analyses, are limited by their specificity, sensitivity, invasiveness, and/or their cost. As such, highly specific and sensitive procedures that would operate by way of detecting novel markers in cells, tissues, or bodily fluids, with minimal invasiveness and at a reasonable cost, would be highly desirable.
Accordingly, there is a great need for more sensitive and accurate methods for predicting whether a person is likely to develop ovarian cancer, for diagnosing ovarian cancer, for monitoring the progression of the disease, for staging the ovarian cancer, for determining whether the ovarian cancer has metastasized, for imaging the ovarian cancer and for better treatment of ovarian cancer.
Colon Cancer
Colorectal cancer is the second most common cause of cancer death in the United States and the third most prevalent cancer in both men and women. M. L. Davila & A. D. Davila, Screening for Colon and Rectal Cancer, in Colon and Rectal Cancer 47 (Peter S. Edelstein ed., 2000). The American Cancer Society estimates that there will be about 106,370 new cases of colon cancer and 40,570 new cases of rectal cancer in the 2004 in the United States alone. Colon cancer and rectal cancer will cause about 56,730 deaths combined in the United States. ACS Website: cancer.org of the world wide web. Nearly all cases of colorectal cancer arise from adenomatous polyps, some of which mature into large polyps, undergo abnormal growth and development, and ultimately progress into cancer. Davila at 55-56. This progression would appear to take at least 10 years in most patients, rendering it a readily treatable form of cancer if diagnosed early, when the cancer is localized. Davila at 56; Walter J. Burdette, Cancer: Etiology, Diagnosis, and Treatment 125 (1998).
Although our understanding of the etiology of colon cancer is undergoing continual refinement, extensive research in this area points to a combination of factors, including age, hereditary and nonhereditary conditions, and environmental/dietary factors. Age is a key risk factor in the development of colorectal cancer, Davila at 48, with men and women over 40 years of age become increasingly susceptible to that cancer, Burdette at 126. Incidence rates increase considerably in each subsequent decade of life. Davila at 48. A number of hereditary and nonhereditary conditions have also been linked to a heightened risk of developing colorectal cancer, including familial adenomatous polyposis (FAP), hereditary nonpolyposis colorectal cancer (Lynch syndrome or HNPCC), a bowel disease, diabetes mellitus, and obesity. Id. at 47; Henry T. Lynch & Jane F. Lynch, Hereditary Nonpolyposis Colorectal Cancer (Lynch Syndromes), in Colon and Rectal Cancer 67-68 (Peter S. Edelstein ed., 2000).
Environmental/dietary factors associated with an increased risk of colorectal cancer include a high fat diet, intake of high dietary red meat, and sedentary lifestyle. Davila at 47; Reddy, B. S., Prev. Med. 16(4): 460-7 (1987). Conversely, environmental/dietary factors associated with a reduced risk of colorectal cancer include a diet high in fiber, folic acid, calcium, and hormone-replacement therapy in post-menopausal women. Davila at 50-55. The effect of antioxidants in reducing the risk of colon cancer is unclear. Davila at 53.
Because colon cancer is highly treatable when detected at an early, localized stage, screening should be a part of routine care for all adults starting at age 50, especially those with first-degree relatives with colorectal cancer. One major advantage of colorectal cancer screening over its counterparts in other types of cancer is its ability to not only detect precancerous lesions, but to remove them as well. Davila at 56. The key colorectal cancer screening tests in use today are fecal occult blood test, sigmoidoscopy, colonoscopy, double-contrast barium enema, and the carcinoembryonic antigen (CEA) test. Burdette at 125; Davila at 56.
The fecal occult blood test (FOBT) screens for colorectal cancer by detecting the amount of blood in the stool, the premise being that neoplastic tissue, particularly malignant tissue, bleeds more than typical mucosa, with the amount of bleeding increasing with polyp size and cancer stage. Davila at 56-57. While effective at detecting early stage tumors, FOBT is unable to detect adenomatous polyps (premalignant lesions), and, depending on the contents of the fecal sample, is subject to rendering false positives. Davila at 56-59. Sigmoidoscopy and colonoscopy, by contrast, allow direct visualization of the bowel, and enable one to detect, biopsy, and remove adenomatous polyps. Davila at 59-60, 61. Despite the advantages of these procedures, there are accompanying downsides: sigmoidoscopy, by definition, is limited to the sigmoid colon and below, colonoscopy is a relatively expensive procedure, and both share the risk of possible bowel perforation and hemorrhaging. Davila at 59-60. Double-contrast barium enema (DCBE) enables detection of lesions better than FOBT, and almost as well a colonoscopy, but it may be limited in evaluating the winding rectosigmoid region. Davila at 60. The CEA blood test, which involves screening the blood for carcinoembryonic antigen, shares the downside of FOBT, in that it is of limited utility in detecting colorectal cancer at an early stage. Burdette at 125.
Once colon cancer has been diagnosed, treatment decisions are typically made in reference to the stage of cancer progression. A number of techniques are employed to stage the cancer (some of which are also used to screen for colon cancer), including pathologic examination of resected colon, sigmoidoscopy, colonoscopy, and various imaging techniques. AJCC Cancer Staging Handbook 84 (Irvin D. Fleming et al. eds., 5th ed. 1998); Montgomery, R. C. and Ridge, J. A., Semin. Surg. Oncol. 15(3): 143-150 (1998). Moreover, chest films, liver functionality tests, and liver scans are employed to determine the extent of metastasis. Fleming at 84. While computerized tomography and magnetic resonance imaging are useful in staging colorectal cancer in its later stages, both have unacceptably low staging accuracy for identifying early stages of the disease, due to the difficulty that both methods have in (1) revealing the depth of bowel wall tumor infiltration and (2) diagnosing malignant adenopathy. Thoeni, R. F., Radiol. Clin. N. Am. 35(2): 457-85 (1997). Rather, techniques such as transrectal ultrasound (TRUS) are preferred in this context, although this technique is inaccurate with respect to detecting small lymph nodes that may contain metastases. David Blumberg & Frank G. Opelka, Neoadjuvant and Adjuvant Therapy for Adenocarcinoma of the Rectum, in Colon and Rectal Cancer 316 (Peter S. Edelstein ed., 2000).
Several classification systems have been devised to stage the extent of colorectal cancer, including the Dukes' system and the more detailed International Union against Cancer-American Joint Committee on Cancer TNM staging system, which is considered by many in the field to be a more useful staging system. Burdette at 126-27. The TNM system, which is used for either clinical or pathological staging, is divided into four stages, each of which evaluates the extent of cancer growth with respect to primary tumor (T), regional lymph nodes (N), and distant metastasis (M). Fleming at 84-85. The system focuses on the extent of tumor invasion into the intestinal wall, invasion of adjacent structures, the number of regional lymph nodes that have been affected, and whether distant metastasis has occurred. Fleming at 81.
Stage 0 is characterized by in situ carcinoma (Tis), in which the cancer cells are located inside the glandular basement membrane (intraepithelial) or lamina propria (intramucosal). In this stage, the cancer has not spread to the regional lymph nodes (N0), and there is no distant metastasis (M0). In stage I, there is still no spread of the cancer to the regional lymph nodes and no distant metastasis, but the tumor has invaded the submucosa (T1) or has progressed further to invade the muscularis propria (T2). Stage II also involves no spread of the cancer to the regional lymph nodes and no distant metastasis, but the tumor has invaded the subserosa, or the nonperitonealized pericolic or perirectal tissues (T3), or has progressed to invade other organs or structures, and/or has perforated the visceral peritoneum (T4). Stage III is characterized by any of the T substages, no distant metastasis, and either metastasis in 1 to 3 regional lymph nodes (N1) or metastasis in four or more regional lymph nodes (N2). Lastly, stage IV involves any of the T or N substages, as well as distant metastasis. Fleming at 84-85; Burdette at 127.
Currently, pathological staging of colon cancer is preferable over clinical staging as pathological staging provides a more accurate prognosis. Pathological staging typically involves examination of the resected colon section, along with surgical examination of the abdominal cavity. Fleming at 84. Clinical staging would be a preferred method of staging were it at least as accurate as pathological staging, as it does not depend on the invasive procedures of its counterpart.
Turning to the treatment of colorectal cancer, surgical resection results in a cure for roughly 50% of patients. Irradiation is used both preoperatively and postoperatively in treating colorectal cancer. Chemotherapeutic agents, particularly 5-fluorouracil, are also powerful weapons in treating colorectal cancer. Other agents include irinotecan and floxuridine, cisplatin, levamisole, methotrexate, interferon-α, and leucovorin. Burdette at 125, 132-33. Nonetheless, thirty to forty percent of patients will develop a recurrence of colon cancer following surgical resection, which in many patients is the ultimate cause of death. Wayne De Vos, Follow-up After Treatment of Colon Cancer, Colon and Rectal Cancer 225 (Peter S. Edelstein ed., 2000). Accordingly, colon cancer patients must be closely monitored to determine response to therapy and to detect persistent or recurrent disease and metastasis.
The next few paragraphs describe the some of molecular bases of colon cancer. In the case of FAP, the tumor suppressor gene APC (adenomatous polyposis coli), chromosomally located at 5q21, has been either inactivated or deleted by mutation. Alberts et al., Molecular Biology of the Cell 1288 (3d ed. 1994). The APC protein plays a role in a number of functions, including cell adhesion, apoptosis, and repression of the c-myc oncogene. N. R. Hall & R. D. Madoff, Genetics and the Polyp-Cancer Sequence, Colon and Rectal Cancer 8 (Peter S. Edelstein, ed., 2000). Of those patients with colorectal cancer who have normal APC genes, over 65% have such mutations in the cancer cells but not in other tissues. Alberts et al., supra at 1288. In the case of HPNCC, patients manifest abnormalities in the tumor suppressor gene HNPCC, but only about 15% of tumors contain the mutated gene. Id. A host of other genes have also been implicated in colorectal cancer, including the K-ras, N-ras, H-ras and c-myc oncogenes, and the tumor suppressor genes DCC (deleted in colon carcinoma) and p53. Hall & Madoff, supra at 8-9; Alberts et al., supra at 1288.
Abnormalities in Wg/Wnt signal transduction pathway are also associated with the development of colorectal carcinoma. Taipale, J. and Beachy, P. A. Nature 411: 349-354 (2001). Wnt1 is a secreted protein gene originally identified within mouse mammary cancers by its insertion into the mouse mammary tumor virus (MMTV) gene. The protein is homologous to the wingless (Wg) gene product of Drosophila, in which it functions as an important factor for the determination of dorsal-ventral segmentation and regulates the formation of fly imaginal discs. Wg/Wnt pathway controls cell proliferation, death and differentiation. Taipal (2001). There are at least 13 members in the Wnt family. These proteins have been found expressed mainly in the central nervous system (CNS) of vertebrates as well as other tissues such as mammary and intestine. The Wnt proteins are the ligands for a family of seven transmembrane domain receptors related to the Frizzled gene product in Drosophila. Binding Wnt to Frizzled stimulates the activity of the downstream target, Dishevelled, which in turn inactivates the glycogen synthesase kinase 3β (GSK3β). Taipal (2001). Usually active GSK3β will form a complex with the adenomatous polyposis coli (APC) protein and phosphorylate another complex member, β-catenin. Once phosphorylated, β-catenin is directed to degradation through the ubiquitin pathway. When GSK3β, or APC activity is down regulated, α-catenin is accumulated in the cytoplasm and binds to the T-cell factor or lymphocyte excitation factor (Tcf/Lef) family of transcriptional factors. Binding of α-catenin to Tcf releases the transcriptional repression and induces gene transcription. Among the genes regulated by β-catenin are a transcriptional repressor Engrailed, a transforming growth factor-β, (TGF-β) family member Decapentaplegic, and the cytokine Hedgehog in Drosophila. β-Catenin also involves in regulating cell adhesion by binding to α-catenin and E-cadherin. On the other hand, binding of β-catenin to these proteins controls the cytoplasmic β-catenin level and its complexing with TCF. Taipal (2001). Growth factor stimulation and activation of c-src or v-src also regulate β-catenin level by phosphorylation of α-catenin and its related protein, p120cas. When phosphorylated, these proteins decrease their binding to E-cadherin and β-catenin resulting in the accumulation of cytoplasmic β-catenin. Reynolds, A. B. et al. Mol. Cell Biol. 14: 8333-8342 (1994). In colon cancer, c-src enzymatic activity has been shown increased to the level of v-src. Alternation of components in the Wg/Wnt pathway promotes colorectal carcinoma development. The best known modifications are to the APC gene. Nicola S et al. Hum. Mol. Genet 10:721-733 (2001). This germline mutation causes the appearance of hundreds to thousands of adenomatous polyps in the large bowel. It is the gene defect that accounts for the autosomally dominantly inherited FAP and related syndromes. The molecular alternations that occur in this pathway largely involve deletions of alleles of tumor-suppressor genes, such as APC, p53 and Deleted in Colorectal Cancer (DCC), combined with mutational activation of proto-oncogenes, especially c-Ki-ras. Aoki, T. et al. Human Mutat. 3: 342-346 (1994). All of these lead to genomic instability in colorectal cancers.
Another source of genomic instability in colorectal cancer is the defect of DNA mismatch repair (MMR) genes. Human homologues of the bacterial mutHLS complex (hMSH2, hMLH1, hPMS1, hPMS2 and hMSH6), which is involved in the DNA mismatch repair in bacteria, have been shown to cause the HNPCC (about 70-90% HNPCC) when mutated. Modrich, P. and Lahue, R. Ann Rev. Biochem. 65: 101-133 (1996); and Peltomäki, P. Hum. Mol. Genet 10: 735-740 (2001). The inactivation of these proteins leads to the accumulation of mutations and causes genetic instability that represents errors in the accurate replication of the repetitive mono-, di-, tri- and tetra-nucleotide repeats, which are scattered throughout the genome (microsatellite regions). Jass, J. R. et al. J. Gastroenterol Hepatol 17: 17-26 (2002). Like in the classic FAP, mutational activation of c-Ki-ras is also required for the promotion of MSI in the alternative HNPCC. Mutations in other proteins such as the tumor suppressor protein phosphatase PTEN (Zhou, X. P. et al. Hum. Mol. Genet 11: 445-450 (2002)), BAX (Buttler, L. M. Aus. N. Z. J. Surg. 69: 88-94 (1999)), Caspase-5 (Planck, M. Cancer Genet Cytogenet. 134: 46-54 (2002)), TGFβ-RII (Fallik, D. et al. Gastroenterol Clin Biol. 24: 917-22 (2000)) and IGFII-R (Giovannucci E. J. Nutr. 131: 3109S-20S (2001)) have also been found in some colorectal tumors possibly as the cause of MMR defect.
Some tyrosine kinases have been shown up-regulated in colorectal tumor tissues or cell lines like HT29. Skoudy, A. et al. Biochem J. 317 (Pt 1): 279-84 (1996). Focal adhesion kinase (FAK) and its up-stream kinase c-src and c-yes in colonic epithelia cells may play an important role in the promotion of colorectal cancers through the extracellular matrix (ECM) and integrin-mediated signaling pathways. Jessup, J. M. et al., The molecular biology of colorectal carcinoma, in: The Molecular Basis of Human Cancer, 251-268 (Coleman W. B. and Tsongalis G. J. Eds. 2002). The formation of c-src/FAK complexes may coordinately deregulate VEGF expression and apoptosis inhibition. Recent evidences suggest that a specific signal-transduction pathway for cell survival that implicates integrin engagement leads to FAK activation and thus activates PI-3 kinase and akt. In turn, akt phosphorylates BAD and blocks apoptosis in epithelial cells. The activation of c-src in colon cancer may induce VEGF expression through the hypoxia pathway. Other genes that may be implicated in colorectal cancer include Cox enzymes (Ota, S. et al. Aliment Pharmacol. Ther. 16 (Suppl 2): 102-106 (2002)), estrogen (al-Azzawi, F. and Wahab, M. Climacteric 5: 3-14 (2002)), peroxisome proliferator-activated receptor-γ (PPAR-γ) (Gelman, L. et al. Cell Mol. Life Sci. 55: 932-943 (1999)), IGF-I (Giovannucci (2001)), thymine DNA glycosylase (TDG) (Hardeland, U. et al. Prog. Nucleic Acid Res. Mol. Biol. 68: 235-253 (2001)) and EGF (Mendelsohn, J. Endocrine-Related Cancer 8: 3-9 (2001)).
Gene deletion and mutation are not the only causes for development of colorectal cancers. Epigenetic silencing by DNA methylation also accounts for the lost of function of colorectal cancer suppressor genes. A strong association between MSI and CpG island methylation has been well characterized in sporadic colorectal cancers with high MSI but not in those of hereditary origin. In one experiment, DNA methylation of MLH1, CDKN2A, MGMT, THBS1, RARB, APC, and p14ARF genes has been shown in 80%, 55%, 23%, 23%, 58%, 35%, and 50% of 40 sporadic colorectal cancers with high MSI respectively. Yamamoto, H. et al. Genes Chromosomes Cancer 33: 322-325 (2002); and Kim, K. M. et al. Oncogene. 12;21(35): 5441-9 (2002). Carcinogen metabolism enzymes such as GST, NAT, CYP and MTHFR are also associated with an increased or decreased colorectal cancer risk. Pistorius, S. et al. Kongressbd Dtsch Ges Chir Kongr 118: 820-824 (2001); and Potter, J. D. J. Natl. Cancer Inst. 91: 916-932 (1999).
From the foregoing, it is clear that procedures used for detecting, diagnosing, monitoring, staging, prognosticating, and preventing the recurrence of colorectal cancer are of critical importance to the outcome of the patient. Moreover, current procedures, while helpful in each of these analyses, are limited by their specificity, sensitivity, invasiveness, and/or their cost. As such, highly specific and sensitive procedures that would operate by way of detecting novel markers in cells, tissues, or bodily fluids, with minimal invasiveness and at a reasonable cost, would be highly desirable.
Accordingly, there is a great need for more sensitive and accurate methods for predicting whether a person is likely to develop colorectal cancer, for diagnosing colorectal cancer, for monitoring the progression of the disease, for staging the colorectal cancer, for determining whether the colorectal cancer has metastasized, and for imaging the colorectal cancer. Following accurate diagnosis, there is also a need for less invasive and more effective treatment of colorectal cancer.
Gastric Cancer
The American Cancer Society estimates that there will be about 22,710 new cases of stomach cancer in 2004 in the United States alone. Stomach cancer will cause about 11,780 deaths in the United States. ACS Website: cancer.org of the world wide web. As recent as 2001 gastric cancer was estimated to rank as the thirteenth most common and the eighth most deadly cancer in the United States. AJCC Cancer Staging Handbook 71 (Irvin D. Fleming et al. eds., 5th ed. 1998). Due to a dramatic decline in the United States over the last four decades, stomach cancer was estimated to account for 2.5% of deaths from cancer in the United States in 1997, with roughly 22,000 new cases and 14,000 deaths estimated for that year. Roderich E. Schwarz, Surgical Management of Gastric Cancer: The Western Experience, in Management of Upper Gastrointestinal Cancer 83-84 (John M. Daly et al. eds. 1999). However, stomach cancer persists in being responsible for considerable mortality rates in Asia, Europe and South America. Walter J. Burdette, Cancer: Etiology, Diagnosis, and Treatment 91 (1998). In Japan for example, gastric cancer accounts for roughly one-half of the cancer deaths in men and one-third of those in women. Id. Overall, patients diagnosed with gastric cancer have an approximate 5-year survival rate of around 25-30%. J. Rüdiger Siewert et al., Early Gastric Cancer, in Management of Upper Gastrointestinal Cancer 136 (John M. Daly et al. eds. 1999).
Although our understanding of the etiology of gastric cancer is undergoing continual refinement, research in this area points to several risk factors, including various stomach diseases, diet, occupation, and genetic factors. Burdette, supra at 91. In the case of stomach diseases, stomach polyps, atrophic gastritis and metaplasia, hyperplasia related to Menetrier's disease, Helicobacter pylori infection, ulcers, and operations to the stomach have all been associated with an increased incidence of stomach cancer. Id. Dietary nitrate ingestion, which results in nitrosamine production in the stomach, as well as the intake of smoked meats, are also suspected as contributing factors. Id.; Fleming et al. eds., supra at 71. From an occupational standpoint, those who work in the metalworking, painting, fishing, ceramic, and printing industries all appear to have an elevated risk of acquiring stomach cancer. Burdette, supra at 91. From a genetic standpoint, gastric carcinomas are believed to occur through two genetic pathways: (1) chromosomal deletions that involve tumor suppressor genes and (2) microsatellite instability which targets the mononucleotide segments in coding regions of genes related to cancer. Rhyu, M. G., J. Korean Med. Sci. 13(4): 339-49 (1998). A variation in the N-acetyltransferase 1 gene has also been linked to elevated risk of gastric cancer. Boissy, R. J. et al., Int'l J. Cancer 87(4): 507-11 (2000).
Like many cancers, gastric cancer is more readily treatable when detected early. Patients diagnosed with early gastric cancer that follow proper treatment have survival rates that match healthy control patients of the same age. Siewert, supra at 136. Unfortunately, the symptoms and clinical manifestations of gastric cancer typically do not appear early in the course of the disease, and the majority of patients have symptoms of the disease for six months or more prior to diagnosis. Burdette, supra at 93. Accordingly, effective screening devices are crucial in diagnosing the disease early and in effecting proper treatment.
Following an initial assessment of a potential gastric cancer patient's symptoms, which may include, inter alia, indigestion, abdominal discomfort, dysphagia, nausea, anorexia, flatulence, weight loss, melena, the presence of a palpable mass, anemia, and enlarged lymph nodes, id., a physician may perform various screening tests. These tests include scanning for the presence of elevated levels of carcinoembryonic and oncofetal antigens, achlorhydria, blood in the stool, and cytologic analysis of gastric washings. Id. Unfortunately, in the case of the first three tests, positive results are not necessarily obtained when gastric cancer is present, or false positives may result due to the presence of other conditions. Id. A certain diagnosis is typically achieved by way of endoscopy and/or radiography using barium contrast medium. Id.; Schwarz, supra at 87. Ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI) are additionally useful in determining the extent of metastasis. Burdette, supra at 94.
Once gastric cancer has been diagnosed, treatment decisions are made in reference to the stage of cancer progression. Iain G. Martin, Staging of Esophageal and Gastric Cancer, in Management of Upper Gastrointestinal Cancer 3 (John M. Daly et al. eds. 1999). Accurate staging has become even more vital to a successful treatment regimen in view of the present trend toward multi-modal therapy for gastric cancer, and particularly neoadjuvant therapy. Id.
A number of techniques are employed to stage gastric cancer (some of which are also used to screen for gastric cancer), including endoscopic ultrasonography (EUS), CT, and MRI. Id. at 24-31. EUS is the only method of staging capable of providing accurate data regarding the tumor stage (T stage) of gastric cancer, and its overall accuracy for gathering data regarding the lymph nodal stage of gastric cancer is about 70% Id. at 27-28. EUS, however, is limited for several reasons: (1) roughly 15% of patients present with non-traversable lesions, (2) there are regions of the stomach in which it is difficult to obtain high quality images, and (3) it has difficulty in discerning particular types of cancerous lesions. Id. at 27. CT scanning is of some utility when used in combination with other techniques, but it is too inaccurate to be used alone for several reasons: (1) it is limited in its ability to assess the tumor stage due to its inability to distinguish between the individual layers of the gastric wall, (2) it is highly inaccurate in assessing lymph node metastasis, and (3) it is generally unhelpful in assessing peritoneal or liver metastasis. Id. at 24, 26-27. MRI, by contrast, is able to distinguish between muscle layers in the stomach, and one study suggests that MRI is able to assist in determining the extent of tumor and serosal invasion with considerable accuracy. Id. at 27. Nonetheless, other studies have indicated that MRI has little to offer to supplement a CT assessment. Id.
The development of staging through the techniques of molecular biology is still in its infancy, but some progress in this area has been made. For example, researchers have found that Thomsen-Friedenreich (TF) and MUC 1-TF immunoreactivity characterizes a high-risk Stage I subgroup of gastric cancer patients. Baldus, S. E. et al., Oncology 61(2): 147-55 (2001). Elevated serum levels of interleukin-2 and tumor necrosis factor-alpha have been studied as possibly useful markers for advanced gastric cancer. Forones, N. M. et al., Hepatogastroenterology 48(40): 1199-201 (2001). Likewise, elevated levels of serum soluble E-cadherin may also serve as a useful prognostic marker for stomach cancer. Chan, A. O. et al., Gut 48(6): 808-11 (2001).
The two major classification systems for staging gastric cancer are the Union Internationale Contre le Cancer's TNM system, and the system devised by the Japanese Research Society for Gastric Cancer. Id. at 18-23. The TNM system is a rather simple, and in some cases arbitrary system, which is divided into several stages, each of which evaluates the extent of cancer growth with respect to primary tumor (T), regional lymph nodes (N), and distant metastasis (M). Id. at 18, 20, 22; Fleming et al. eds., supra at 3. The Japanese system is considerably more detailed, but in some cases may be overly complex and time consuming. Martin, supra at 18-20, 22-23. Because most countries other than Japan have adopted the TNM system, id. at 23, that system will be discussed further here.
Stage 0 is characterized by carcinoma in situ (Tis, an intra-epithelial tumor that has not invaded the lamina propria), and stage IA involves tumor invasion of the lamina propria or submucosa (T1); neither stage involves metastasis to the regional lymph nodes (N0) nor distant metastasis (MO). Fleming et al. eds., supra at 73. Stage IB is the same as stage IA except that either (1) regional lymph node metastasis has occurred in 1 to 6 lymph nodes (N1) or (2) the tumor has invaded the muscularis propria or subserosa (T2). Id. Stage II gastric cancer is a bit more complex than the previous stages, involving one of three scenarios, none of which involve distant metastasis: (1) tumor category T1 and metastasis into 7 to 15 regional lymph nodes (N2), (2) tumor category T2 and nodal category N1, or (3) tumor invasion into serosa without invasion into adjacent structures (i.e., spleen, liver, transverse colon, diaphragm, adrenal gland, kidney, pancreas, small intestine, retroperitoneum, and abdominal wall) and nodal category N0. Id. Stage IIIA likewise involves one of three possible scenarios: (1) tumor category T2 and nodal category N2, (2) tumor category T3 and nodal category N3, or (3) tumor invasion into adjacent structures (T4) and nodal category N0. Id. at 73-74. Stage IIIB, however, involves tumor category T3 and nodal category N2. Id. Neither stage IIIA nor stage IIIB involves distant metastasis. Id. Stage IV is characterized by a variety permutations of tumor and nodal categories, with or without distant metastasis. Id.
Turning to the treatment of gastric cancer, surgical resection is the “mainstay” of treating gastric carcinomas but is only an option for 50% to 60% of patients. David Kelsen, Combined Modality Therapy, in Management of Upper Gastrointestinal Cancer 123 (John M. Daly et al. eds. 1999). While radiotherapy is sometimes used in conjunction with resection with some effect, gastric carcinomas are typically more resistant to radiation than are other carcinomas. Burdette, supra at 97. Likewise, chemotherapy has generally been of limited utility in treating gastric carcinomas, although neoadjuvant and adjuvant chemotherapy have been used with some success. Id. at 98; Schuhmacher, C. P. et al., Cancer 91(5): 918-27 (2001). Pre- or postoperative adjuvant therapy is currently being studied due to the considerable risk for reoccurrence, as well as the fact that systemic metastasis is commonplace. Kelsen, supra at 123. When chemotherapy is used, combinations of chemotherapeutic agents yield better results than single agents; agents used in successful combinations include 5-fluoruracil, leucovorin, adriamycin, cisplatin, mitomycin, etoposide, and semustine. Burdette, supra at 98.
From the foregoing, it is clear that procedures used for detecting, diagnosing, monitoring, staging, prognosticating, treating and preventing the recurrence of gastric cancer are of critical importance to the outcome of the patient. Moreover, current procedures, while helpful in each of these areas, are limited by their specificity, sensitivity, invasiveness, and/or their cost. As such, highly specific and sensitive procedures that would operate by way of detecting novel markers in cells, tissues, or bodily fluids, with minimal invasiveness and at a reasonable cost, would be highly desirable.
Angiogenesis in Cancer
Growth and metastasis of solid tumors are also dependent on angiogenesis. Folkman, J., 1986, Cancer Research, 46, 467-473; Folkman, J., 1989, Journal of the National Cancer Institute, 82, 4-6. It has been shown, for example, that tumors which enlarge to greater than 2 mm must obtain their own blood supply and do so by inducing the growth of new capillary blood vessels. Once these new blood vessels become embedded in the tumor, they provide a means for tumor cells to enter the circulation and metastasize to distant sites such as liver, lung or bone. Weidner, N., et al., 1991, The New England Journal of Medicine, 324(1), 1-8.
Angiogenesis, defined as the growth or sprouting of new blood vessels from existing vessels, is a complex process that primarily occurs during embryonic development. The process is distinct from vasculogenesis, in that the new endothelial cells lining the vessel arise from proliferation of existing cells, rather than differentiating from stem cells. The process is invasive and dependent upon proteolysis of the extracellular matrix (ECM), migration of new endothelial cells, and synthesis of new matrix components. Angiogenesis occurs during embryogenic development of the circulatory system; however, in adult humans, angiogenesis only occurs as a response to a pathological condition (except during the reproductive cycle in women).
Under normal physiological conditions in adults, angiogenesis takes place only in very restricted situations such as hair growth and wounding healing. Auerbach, W. and Auerbach, R., 1994, Pharmacol Ther. 63(3):265-3 11; Ribatti et al., 1991, Haematologica 76(4):3 11-20; Risau, 1997, Nature 386(6626):67 1-4. Angiogenesis progresses by a stimulus which results in the formation of a migrating column of endothelial cells. Proteolytic activity is focused at the advancing tip of this “vascular sprout”, which breaks down the ECM sufficiently to permit the column of cells to infiltrate and migrate. Behind the advancing front, the endothelial cells differentiate and begin to adhere to each other, thus forming a new basement membrane. The cells then cease proliferation and finally define a lumen for the new arteriole or capillary.
Unregulated angiogenesis has gradually been recognized to be responsible for a wide range of disorders, including, but not limited to, cancer, cardiovascular disease, rheumatoid arthritis, psoriasis and diabetic retinopathy. Folkman, 1995, Nat Med 1(1):27-31; Isner, 1999, Circulation 99(13): 1653-5; Koch, 1998, Arthritis Rheum 41(6):951-62; Walsh, 1999, Rheumatology (Oxford) 38(2):103-12; Ware and Simons, 1997, Nat Med 3(2): 158-64.
Of particular interest is the observation that angiogenesis is required by solid tumors for their growth and metastases. Folkman, 1986 supra; Folkman 1990, J. Natl. Cancer Inst., 82(1) 4-6; Folkman, 1992, Semin Cancer Biol 3(2):65-71; Zetter, 1998, Annu Rev Med 49:407-24. A tumor usually begins as a single aberrant cell which can proliferate only to a size of a few cubic millimeters due to the distance from available capillary beds, and it can stay ‘dormant’ without further growth and dissemination for a long period of time. Some tumor cells then switch to the angiogenic phenotype to activate endothelial cells, which proliferate and mature into new capillary blood vessels. These newly formed blood vessels not only allow for continued growth of the primary tumor, but also for the dissemination and recolonization of metastatic tumor cells. The precise mechanisms that control the angiogenic switch is not well understood, but it is believed that neovascularization of tumor mass results from the net balance of a multitude of angiogenesis stimulators and inhibitors Folkman, 1995, supra.
One of the most potent angiogenesis inhibitors is endostatin identified by O'Reilly and Folkman. O'Reilly et al., 1997, Cell 88(2):277-85; O'Reilly et al., 1994, Cell 79(2):315-28. Its discovery was based on the phenomenon that certain primary tumors can inhibit the growth of distant metastases. O'Reilly and Folkman hypothesized that a primary tumor initiates angiogenesis by generating angiogenic stimulators in excess of inhibitors. However, angiogenic inhibitors, by virtue of their longer half life in the circulation, reach the site of a secondary tumor in excess of the stimulators. The net result is the growth of primary tumor and inhibition of secondary tumor. Endostatin is one of a growing list of such angiogenesis inhibitors produced by primary tumors. It is a proteolytic fragment of a larger protein: endostatin is a 20 kDa fragment of collagen XVIII (amino acid H1132-K1315 in murine collagen XVIII). Endostatin has been shown to specifically inhibit endothelial cell proliferation in vitro and block angiogenesis in vivo. More importantly, administration of endostatin to tumor-bearing mice leads to significant tumor regression, and no toxicity or drug resistance has been observed even after multiple treatment cycles. Boehm et al., 1997, Nature 390(6658):404-407. The fact that endostatin targets genetically stable endothelial cells and inhibits a variety of solid tumors makes it a very attractive candidate for anticancer therapy. Fidler and Ellis, 1994, Cell 79(2):185-8; Gastl et al., 1997, Oncology 54(3):177-84; Hinsbergh et al., 1999, Ann Oncol 10 Suppl 4:60-3. In addition, angiogenesis inhibitors have been shown to be more effective when combined with radiation and chemotherapeutic agents. Klement, 2000, J. Clin Invest, 105(8) R15-24. Browder, 2000, Cancer Res. 6-(7) 1878-86, Arap et al., 1998, Science 279(5349):377-80; Mauceri et al., 1998, Nature 394(6690):287-91.
The present invention provides alternative methods of assessing risk of, detecting or treating prostate, ovarian, colon, breast and stomach cancer that overcome the limitations of conventional therapeutic methods as well as offer additional advantages that will be apparent from the detailed description below.